1. Field of the Invention
The present invention relates to a thyristor device and particularly to a thyristor device providing a protection means which protects a thyristor from an external surge.
2. Description of the Prior Art
A device shown in FIG. 1 has been proposed as a thyristor device of this type. FIG. 1 is a block connection diagram indicating a thyristor device, in which numeral 1 denotes a thyristor, 2 is a protection element connected in parallel to the thyristor 1 through the connecting conductors 3, 4. Numeral 5 is an object to be controlled by the thyristor, and this control object 5 and thyristor 1 are connected through the connecting conductors 6, 7. The protection element 2 forms a so-called surge absorption circuit and is composed of an RC circuit and an avalanche diode as the non-linear element. Particularly, if a control object is an inductive load such as a motor, a flywheel diode, for example, is used as the protection element. Moreover, a lead or cable having a constant current capacity is used as the connecting conductors 3, 4, 6 and 7.
Operations of the device shown in FIG. 1 are explained. It is assumed that a surge or short-circuit of control object 5 is generated when a lightning surge occurs or the switch is opened or closed. In this case, a surge voltage reaches the thyristor 1 through the connecting conductors 6, 7 from the control object 5. Thereby, the protection element 2 absorbs such surge voltage in order to prevent breakdown of thyristor 1.
The thyristor device of the prior art providing a protection device is constituted as explained above and therefore there has arisen a problem that a surge current coming from the side of control object 5 flows into the connecting conductors 3, 4 such as lead wire and cable which connects the thyristor 1 and protection element 2 causing a risk of inductive interference on the electrical circuits near these connecting conductors 3, 4 and therefore the thyristor device has to be located apart from the electrical circuits in order to avoid such inductive interference. Moreover, this thyristor device has a disadvantage that the device as a whole including a thyristor 1, a protection element 2 and connecting conductors 3, 4, 6, and 7 occupies a large space.